It is known to use diptanks to apply photoreceptor coating solution to photoreceptor devices. Once inserted in the diptanks, the devices will be removed from the diptank with a controlled speed, and a thin layer of photoreceptor coating becomes coated upon each device.
Typically the diptank will create a coating solution overflow return that flows to a reservoir by means of a return line. Later, this returned coating solution in the reservoir will be filtered and pumped back to the diptank.
The typical return line discharges the coating solution overflow return into the reservoir at a fixed vertical height or level with respect the surface of the reservoir. This fixed-height discharge approach creates problems. If the solution overflow return discharge level is set too low with respect to the surface of the reservoir such as, for example, when the solution overflow return discharge is near the reservoir tank bottom, the discharged solution will not mix well. On the other hand, if the solution overflow return discharge level is set too high with respect to the surface of the reservoir such as, for example, when the solution overflow return discharge is a substantial height above the surface, then the solution overflow return discharge will spread on the surface of the surface of the reservoir and create bubbles. These bubbles are not desired, as they will create coating defects in the finished photoreceptor devices.
In another aspect of the invention, there is described a self-adjusting return line for use with a diptank for applying coating solution to devices that are dipped therein and a reservoir tank containing a reservoir of coating solution, the diptank forming a coating solution overflow return that flows to the coating solution reservoir by means of a conduit and the self-adjusting return line, the self-adjusting return line comprising a tubing that includes an upper portion, a central portion and a lower portion, the upper portion coupled to the conduit, the central portion arranged to extend and compress in its length, the lower portion supported by an attached buoy that floats on a surface of the reservoir, the lower portion defining an outlet for discharging the coating solution overflow return to the reservoir.